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Helminthiasis, also known as worm infection, is any macroparasite disease of humans and other animals in which a part of the body is infected with parasitism , known as helminths. There are numerous species of these , which are broadly classified into cestoda, trematoda, and nematode. They often live in the gastrointestinal tract of their hosts, but they may also burrow into other organs, where they induce physiological damage.
Soil-transmitted helminthiasis and schistosomiasis are the most important helminthiases, and are among the neglected tropical diseases. These group of helminthiases have been targeted under the joint action of the world's leading pharmaceutical companies and non-governmental organizations through a project launched in 2012 called the London Declaration on Neglected Tropical Diseases, which aimed to control or eradicate certain neglected tropical diseases by 2020.
Helminthiasis has been found to result in poor birth outcome, poor cognitive development, poor school and work performance, poor socioeconomic development, and poverty.Report of a WHO Expert Committee (1987). Prevention and Control of Intestinal Parasitic Infections. World Health Organization, Technical Report Series 749.Del Rosso, Joy Miller and Tonia Marek (1996). Class Action: Improving School Performance in the Developing World through Better Health and Nutrition. The World Bank, Directions in Development. Chronic illness, malnutrition, and anemia are further examples of secondary effects.
Soil-transmitted helminthiases are responsible for parasitic infections in as much as a quarter of the human population worldwide. One well-known example of soil-transmitted helminthiases is ascariasis.
Helminthiases are classified as follows (the disease names end with "-sis" and the causative worms are in brackets):
Certain worms may cause particular constellations of symptoms. For instance, taeniasis can lead to epilepsy due to neurocysticercosis.
Chronic immune responses to helminthiasis may lead to increased susceptibility to coinfection such as tuberculosis, HIV, and malaria. There is conflicting information about whether deworming reduces HIV progression and viral load and increases CD4 counts in antiretroviral naive and experienced individuals, although the most recent Cochrane review found some evidence that this approach might have favorable effects. Helminth infection also lowers the immune responses to vaccination for other diseases such as BCG vaccine, measles, and Hepatitis B.
Malnutrition due to worms can give rise to anorexia. A study of 459 children in Zanzibar revealed spontaneous increases in appetite after deworming. Anorexia might be a result of the body's immune response and the stress of combating infection. Specifically, some of the cytokines released in the immune response to worm infestation have been linked to anorexia in animals.
The roundworm, Dracunculus has a complex mode of transmission: it is acquired from drinking infested water or eating frogs and fish that contain (had eaten) infected crustaceans (copepods); and can also be transmitted from infected pets (cats and dogs). Roundworms such as Brugia, Wuchereria and Onchocerca are directly transmitted by mosquitoes. In the developing world, the use of contaminated water is a major risk factor for infection. Infection can also take place through the practice of geophagy, which is not uncommon in parts of sub-Saharan Africa. Soil is eaten, for example, by children or pregnant women to counteract a real or perceived deficiency of minerals in their diet.
Further preventive measures include adherence to appropriate food hygiene, wearing of shoes, regular deworming of pets, and the proper disposal of their feces.
Scientists are also searching for a vaccine against helminths, such as a hookworm vaccine.
In 2014–15, the WHO estimated that approximately 2 billion people were infected with soil-transmitted helminthiases, 249 million with schistosomiasis, 56 million people with food-borne trematodiasis, 120 million with lymphatic filariasis, 37 million people with onchocerciasis, and 1 million people with echinococcosis. Another source estimated a much higher figure of 3.5 billion infected with one or more soil-transmitted helminths.Velleman, Y., Pugh, I. (2013). Under-nutrition and water, sanitation and hygiene - Water, sanitation and hygiene (WASH) play a fundamental role in improving nutritional outcomes. A successful global effort to tackle under-nutrition must include WASH. WaterAid and Share, UK
In 2014, only 148 people were reported to have dracunculiasis because of a successful eradication campaign for that particular helminth, which is easier to eradicate than other helminths as it is transmitted only by drinking contaminated water.
Because of their high mobility and lower standards of hygiene, school-age children are particularly vulnerable to helminthiasis. Most children from developing nations will have at least one infestation. Multi-species infections are very common.
The most common intestinal parasites in the United States are Enterobius vermicularis, Giardia lamblia, Ancylostoma duodenale, Necator americanus, and Entamoeba histolytica.
In a developing country like Bangladesh, the most common species are round worm ( Ascaris lumbricoides), whipworm (Tricurias tricuras) and hookworm
(Ancylostoma duodenalis).
The 1990–2013 Global Burden of Disease Study estimated 5,500 direct deaths from schistosomiasis, while more than 200,000 people were estimated in 2013 to die annually from causes related to schistosomiasis. Another 20 million have severe consequences from the disease. It is the most deadly of the neglected tropical diseases.
200,000 indirect deaths from "causes related to" Schistosomiasis
Variations within communities
Even in areas of high prevalence, the frequency and severity of infection is not uniform within communities or families. (2025). 9781416043904, Saunders. ISBN 9781416043904 A small proportion of community members harbour the majority of worms, and this depends on age. The maximum worm burden is at five to ten years of age, declining rapidly thereafter. (2025). 9781416043904, Saunders. ISBN 9781416043904 Individual predisposition to helminthiasis for people with the same sanitation infrastructure and hygiene behavior is thought to result from differing immunocompetence, Human nutrition, and Heredity. Because individuals are predisposed to a high or a low worm burden, the burden reacquired after successful treatment is proportional to that before treatment.
Disability-adjusted life years
It is estimated that intestinal nematode infections cause 5 million disability-adjusted life years (DALYS) to be lost, of which hookworm infections account for more than 3 million DALYS and ascaris infections more than 1 million. There are also signs of progress: The Global Burden of Disease Study published in 2015 estimates a 46 percent (59 percent when age standardised) reduction in years lived with disability (YLD) for the 13-year time period from 1990 to 2013 for all intestinal/nematode infections, and even a 74 percent (80 percent when age standardised) reduction in YLD from ascariasis.
Deaths
As many as 135,000 die annually from soil transmitted helminthiasis.
Soil transmitted helminthiasis (STH) (classified as neglected tropical disease): Ascaris lumbricoides Roundworm 1000 to 1450
807 to 1,121 20,000 Many regions of South-east Asia, Africa, and Central and South America Trichuris trichiura Whipworm 500
604–795 In moist, warm, tropical regions of Asia, Africa, Central and South America, and the Caribbean islands.WHO (2006). WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater – Volume IV: Excreta and greywater use in agriculture . World Health Organization (WHO), Geneva, Switzerland Ancylostoma duodenale Hookworms 900 to 1300
576–740 (hookworm in general) In tropical and subtropical countries (Sub-Saharan Africa) Necator americanus Strongyloides stercoralis Hookworm, pinworm 50 to 100 Thousands In moist rainy areas of the tropics and subtropics, in some areas of southern and eastern Europe and of the United States of America All STH together 1500 to 2000 135,000 Tropical and subtropical areas, in particular sub-Saharan Africa, the Americas, China and east Asia. Not transmitted via soil but classified as neglected tropical disease: Schistosoma mansoni Blood fluke All types of Schistosoma together: 160 to 200
(210 "affected") 12,000 150,000 deaths from kidney failure
In tropical and subtropical regions Schistosoma haematobium 112 (in Sub-Saharan Africa alone)Luke F. Pennington and Michael H. Hsieh (2014) Immune Response to Parasitic Infections , Bentham e books, Vol 2, pp. 93–124, Echinococcus granulosus 3Elisabetta Profumo, Alessandra Ludovisi, Brigitta Buttari, Maria, Angeles Gomez Morales and Rachele Riganò (2014) Immune Response to Parasitic Infections , Bentham e books, Bentham Science Publishers, Vol 2, pp. 69–91, Developing countries Not transmitted via soil and not classified as neglected tropical disease: Toxocara canis Dog roundworm 50 Many regions of South-east Asia, Africa, and Central and South America Taenia solium Pork tapeworm 50 South America, Southeast Asia, West Africa and East Africa Taenia saginata Beef tapeworm 50
(all types of Taenia: 40 to 60 (2025). 9781588902450, Thieme. ISBN 9781588902450) Hymenolepis nana Dwarf tapeworm 100 Hymenolepis diminuta Rat tapeworm Fasciola hepatica,
Fascioloides magnaLiver fluke 50 Largely in southern and eastern Asia but also in central and eastern Europe Fasciolopsis buski Giant intestinal fluke Dracunculus medinensis Guinea worm Negligible thanks to eradication program Formerly widespread in India, west Africa and southern Sudan Trichostrongylus orientalis Roundworm 1–3 ("several") Rural communities in Asia Other 100 Worldwide Total (number of infections) Approx. 3.5 billion Worldwide
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